Life Yesterday. The Geological Column. Dating Rocks

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Rocks can be dated.
Rocks, like everything else, are made of atoms.
When rocks form, some of the atoms in it are radioactive.
When these atoms make radiation, they change.
We can measure the changes and work out when the rocks first formed.

0 half-lives

1 half-life

2 half-lives

3 half-lives

4 half-lives

These atoms radiate and change just by chance,
but we know how long it takes half of them to do it.
The time it takes is called the atom's half-life.
By measuring the radioactive atoms and the changed atoms,
we can work out the age of many rocks.
Some people think that radiation happened much more quickly in the past,
so the age of rocks seem to be much older than they really are.
There is no reason to think this is right though.
One problem with this idea is the amount of radiation it would mean.
Nothing could have lived in that much radiation!